[SyzyAsan] Fix overflow error in ShadowWalker for 4GB 32-bit processes.

syzygy/agent/asan/heap_checker.h

 // Copyright 2014 Google Inc. All Rights Reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
@@ skipping 35 matching lines @@
   //     ranges.
   // @returns true if the heap is corrupt, false otherwise.
   bool IsHeapCorrupt(CorruptRangesVector* corrupt_ranges);
 
   // TODO(sebmarchand): Add a testing seam that controls the range of memory
   //     that is walked by HeapChecker to keep unittest times to something
   //     reasonable.
 
  private:
   // Get the information about the corrupt ranges in a heap slab.
-  // @param lower_bound The lower bound for this slab.
-  // @param length The length of this slab.
+  // @param lower_bound The lower bound for this slab (inclusive).
+  // @param upper_bound The upper bound for this slab (exclusive). An
+  //     overflowed value of 0 indicates the end of all memory.
   // @param corrupt_ranges Will receive the information about the corrupt ranges
   //     in this slab.
   void GetCorruptRangesInSlab(const uint8_t* lower_bound,
-                              size_t length,
+                              const uint8_t* upper_bound,
                               CorruptRangesVector* corrupt_ranges);
 
   // The shadow memory that will be analyzed.
   Shadow* shadow_;
 
   DISALLOW_COPY_AND_ASSIGN(HeapChecker);
 };
 
 }  // namespace asan
 }  // namespace agent
 
 #endif  // SYZYGY_AGENT_ASAN_HEAP_CHECKER_H_